Xenix

Xenix is a proprietary Unix clone made by Microsoft. The reason it exists is because Bell Labs couldn't license it directly to end-users, but it could license it to other companies, who could in turn license it to end-users. The company that they chose for this was Microsoft as, even back then in the 70s, Microsoft was the biggest software company. Though, it didn't have much success because by the time it was licensed, most PCs weren't powerful enough to run unix, so they ran CP/M and then DOS, as it came preinstalled. By the time that most PCs were powerful enough to run Unix, and hence Xenix, most software was made for DOS, and most people couldn't switch to Xenix, as that would wouldnt allow them to run all their DOS software.

XeDOS

XeDOS was originally meant as a stepping stone betwen MS-DOS, which was meant for cheap PCs with few users to Xenix which was meant to be used on multi-user computers.

However, XeDOS was never really published, but some aspects of it were put in MS-DOS 2, such as being able to change the switch argument from /(forwardslash) to -(hyphen) by editing config.sys. Another thing that you could do by editing config.sys in MS-DOS 2 is to change the symbol used for directories from \(backslash) to /(forwardslash), and move a lot of device drivers(such as CON, or AUX, for example. you probably know them because you cannot name files or folders in windows like that) from being universally accesible from every directory, to the /dev/ directory. An example of this is that instead of typing "COPY CON: A:\FILE.TXT", you could type "copy /dev/con file.txt". Though, starting from MS-DOS 3.0, Microsoft removed the ability to do that. This proves that the reason windows uses \ instead of / doesn't have anything to do with backwards compatibility, and is intentional. Coincidentally, this is also when Paul Allen left Microsoft.